The invention relates to a microwave antenna for the generation of an antenna beam with adjustable parameters, provided with an active microwave radiation source, a Fresnel zone plate for generating the antenna beam and display means for displaying the Fresnel zones on the Fresnel zone plate.
Such a microwave antenna is described in WO 93/26059-A1. The antenna described in said document operates in a transmission mode and has the drawback that 3dB of the incident microwave radiation remains unused. In a radar system that incorporates this microwave antenna, this results in a 6 dB system loss, 3 dB at transmission and 3 dB at the reception of radiation reflected by a target. Since microwave antennas of this type are particularly suitable for applications at higher frequencies, where microwave generators are expensive and have a limited power, this 6 dB loss is a serious drawback.
In addition, such losses give often rise to the occurrence of unexpected sidelobes of the antenna system via multiple reflections. It is therefore of particular importance to actually transmit all energy available in the antenna beam.